The directional specular component of the He et al. BSDF model. More...

#include <he.h>

Public Member Functions
	BBM_IMPORT_CONFIG (CONF)

Spectrum	eval (const Vec3d &in, const Vec3d &out, BsdfFlag component=bsdf_flag::All, unit_t=unit_t::Radiance, Mask mask=true) const
	Evaluate the BSDF for a given in and out direction.

BsdfSample	sample (const Vec3d &out, const Vec2d &xi, BsdfFlag component=bsdf_flag::All, unit_t unit=unit_t::Radiance, Mask mask=true) const
	Sample the diffuse BSDF given a direction and two random variables.

Value	pdf (const Vec3d &in, const Vec3d &out, BsdfFlag component=bsdf_flag::All, unit_t unit=unit_t::Radiance, Mask mask=true) const
	Compute the pdf given an in and out direction.

Spectrum	reflectance (const Vec3d &out, BsdfFlag component=bsdf_flag::All, unit_t=unit_t::Radiance, Mask mask=true) const
	Return the (approximate) hemispherical reflectance of the BSDF.

	BBM_DEFAULT_CONSTRUCTOR (he_base)
	Default Constructor.

Public Attributes
	BBM_BSDF_FORWARD

Static Public Attributes
static constexpr string_literal	name = NAME

Private Member Functions
constexpr Value	S (const Vec3d &in, const Vec3d &out, Mask mask=true) const
	Shadowing term.

constexpr Value	S1 (const Vec3d &v, Mask mask=true) const
	Mono-directional shadowing term.

constexpr Value	G (const Vec3d &in, const Vec3d &out, Mask mask=true) const
	Compute the Geometrical factor.

constexpr Value	sigma (const Vec3d &in, const Vec3d &out, Mask mask=true) const
	Compute the effective surface roughness.

constexpr Spectrum	D (const Vec3d &in, const Vec3d &out, Mask mask=true) const
	Distribution Function.

Class Attributes
bsdf_parameter< Value, bsdf_attr::SpecularParameter, 0.18 >	roughness

bsdf_parameter< Value, bsdf_attr::SpecularParameter, 3.0 >	autocorrelation

fresnel_parameter< typename std::decay_t< Fresnel >::parameter_type >	eta

	BBM_ATTRIBUTES (roughness, autocorrelation, eta)

Detailed Description

template<typename CONF, typename Fresnel = fresnel::complex<CONF, Spectrum_t<CONF>>, he_eq25 EQ25 = he_eq25::WithoutExp, he_eq78 EQ78 = he_eq78::Regular, size_t NewtonRaphsonSteps = 4, size_t TaylorTerms = 40, bool AdaptiveTaylor = true, literal RoughApproxThreshold = std::numeric_limits<Scalar_t<CONF>>::max(), string_literal NAME = "He">
requires concepts::config<CONF> && concepts::fresnel<Fresnel> && concepts::matching_config<CONF, Fresnel>
class bbm::he_base< CONF, Fresnel, EQ25, EQ78, NewtonRaphsonSteps, TaylorTerms, AdaptiveTaylor, RoughApproxThreshold, NAME >

The directional specular component of the He et al. BSDF model.

Template Parameters

CONF	= bbm configuration
Fresnel	= fresnel implementation (requires concepts::fresnel); default = fresnel::complex
EQ25	= determines whether or not to include an extra scaling factor in Eq 25. (Default = he_eq25::WithoutExp)
EQ78	= determines which implementation variant to follow for Eq ( Default=he_eq78::Regular)
NewtonRaphsonSteps	= number of Newton Raphson steps to take to compute the apparent roughness (Default=4)
TaylorTerms	= number of terms in the Taylor expansion for Eq. 78. (Default=40)
AdaptiveTaylor	= true if the Talylor approximation should be cut of if the change with additional terms is minimal. If false, all 'TaylorTerms' terms will be computed. (Default = true).
RoughApproxThreshold	= 'g' threshold at which the use an approximation instead of the Taylor series. Both solutions are linearly blended within g and g+1. (Default=disabled).
NAME	= model name (default = "He")

Note: the default settings best approximate the original formulation in He et al. 1991

Note: this only implements the directional specular component

Implements: concepts::bsdfmodel

Member Function Documentation

◆ BBM_ATTRIBUTES()

BBM_ATTRIBUTES	(	roughness	,
		autocorrelation	,
		eta
	)

◆ BBM_DEFAULT_CONSTRUCTOR()

BBM_DEFAULT_CONSTRUCTOR ( he_base< CONF, Fresnel, EQ25, EQ78, NewtonRaphsonSteps, TaylorTerms, AdaptiveTaylor, RoughApproxThreshold, NAME > )

inline

Default Constructor.

◆ BBM_IMPORT_CONFIG()

BBM_IMPORT_CONFIG ( CONF )

◆ D()

constexpr Spectrum D	(	const Vec3d &	in,
		const Vec3d &	out,
		Mask	mask = `true`
	)		const

inlineconstexprprivate

Distribution Function.

Eq. 78 & 79

Note Westin et al. uses exp(-g - v_xy2 * (tau/lambda)^2 * Pi^2 / m) instead of exp(-g - v_xy2 * tau^2 / (4m)). This behavior can be set with the EQ78 template parameter (he_eq78::Westin).

◆ eval()

Spectrum eval	(	const Vec3d &	in,
		const Vec3d &	out,
		BsdfFlag	component = `bsdf_flag::All`,
		unit_t	= `unit_t::Radiance`,
		Mask	mask = `true`
	)		const

inline

Evaluate the BSDF for a given in and out direction.

Parameters

in	= incident direction
out	= outgoing direction
component	= which reflectance component to eval
unit	= unit of computation (ignored)
mask	= masking of lanes (e.g., for Packet eval)

Returns: Evaluation of the BSDF per spectrum.

◆ G()

constexpr Value G	(	const Vec3d &	in,
		const Vec3d &	out,
		Mask	mask = `true`
	)		const

inlineconstexprprivate

Compute the Geometrical factor.

Eq. 76 in [He et al. 1991]

Note: k_i = -in k_r = out

Parameters

in	= incident direction of light transport
out	= outgoing direction of light transport
mask	= enable/disbale lanes

Returns: the geometrical factor

◆ pdf()

Value pdf	(	const Vec3d &	in,
		const Vec3d &	out,
		BsdfFlag	component = `bsdf_flag::All`,
		unit_t	unit = `unit_t::Radiance`,
		Mask	mask = `true`
	)		const

inline

Compute the pdf given an in and out direction.

Parameters

in	= the incoming direction
out	= the outgoing direction
component	= which reflectance component was sampled
unit	= unit of computation
mask	= enable/disable lanes.

Returns: the PDF that the outgoing direction would be sampled given the incoming direction.

◆ reflectance()

Spectrum reflectance	(	const Vec3d &	out,
		BsdfFlag	component = `bsdf_flag::All`,
		unit_t	= `unit_t::Radiance`,
		Mask	mask = `true`
	)		const

inline

Return the (approximate) hemispherical reflectance of the BSDF.

Parameters

out	= the outgoing direction (ignored)
component	= which reflectance component to eval
unit	= unit of computation
mask	= enable/disable lanes

Returns: the approximate hemispherical reflectance of the BSDF for a given incident direction

◆ S()

constexpr Value S	(	const Vec3d &	in,
		const Vec3d &	out,
		Mask	mask = `true`
	)		const

inlineconstexprprivate

Shadowing term.

Parameters

in	= incident direction of light transport
out	= exitant direction of light transport
mask	= enable/disable lanes

Returns: fraction of surface visible and illuminated.

◆ S1()

constexpr Value S1	(	const Vec3d &	v,
		Mask	mask = `true`
	)		const

inlineconstexprprivate

Mono-directional shadowing term.

Eqs. 24 and 25 from [He et al. 1991]

Parameters

v	= indident/outgoing vector

Returns: fraction of surface viewed/illuminated

He et al.'s paper [1991] misses an exponential exp(-(tau*cot/2sigma0)^2) term in Eq. 25 (noted in the errata, and by both Westin et al. and Holzschuch and Pacanowski). Set template EQ25 to he_eq25::Errata to include this factor.

◆ sample()

BsdfSample sample	(	const Vec3d &	out,
		const Vec2d &	xi,
		BsdfFlag	component = `bsdf_flag::All`,
		unit_t	unit = `unit_t::Radiance`,
		Mask	mask = `true`
	)		const

inline

Sample the diffuse BSDF given a direction and two random variables.

Parameters

out	= outgoing direction
xi	= two random variables stored in a Vec2d
component	= which reflectance component to sample
unit	= unit of computation (ignored)
mask	= masking of lanes.

Returns: A bsdfSample containing the sampled direction and the corresponding pdf.

◆ sigma()

constexpr Value sigma	(	const Vec3d &	in,
		const Vec3d &	out,
		Mask	mask = `true`
	)		const

inlineconstexprprivate

Compute the effective surface roughness.

Eq. 80 from [He et al. 1991]. This equation is solved with a Newton-Raphson root finding.

Parameters

in	= incident direction of light transport
out	= outgoing direction of light transport
mask	= enable/disbale lanes

Returns: the apparent roughness

Member Data Documentation

◆ autocorrelation

bsdf_parameter<Value, bsdf_attr::SpecularParameter, 3.0> autocorrelation

◆ BBM_BSDF_FORWARD

BBM_BSDF_FORWARD

◆ eta

fresnel_parameter<typename std::decay_t<Fresnel>::parameter_type> eta

◆ name

constexpr string_literal name = NAME

staticconstexpr

◆ roughness

bsdf_parameter<Value, bsdf_attr::SpecularParameter, 0.18> roughness

The documentation for this class was generated from the following file:

include/bsdfmodel/he.h

Public Member Functions

Public Attributes

Static Public Attributes

Private Member Functions

Class Attributes

Detailed Description

Member Function Documentation

◆ BBM_ATTRIBUTES()

◆ BBM_DEFAULT_CONSTRUCTOR()

◆ BBM_IMPORT_CONFIG()

◆ D()

◆ eval()

◆ G()

◆ pdf()

◆ reflectance()

◆ S()

◆ S1()

◆ sample()

◆ sigma()

Member Data Documentation

◆ autocorrelation

◆ BBM_BSDF_FORWARD

◆ eta

◆ name

◆ roughness